1. Field of the Invention
The present invention relates to an exhaust emission control device for removing components having an offensive odor and particulates contained in an exhaust gas of a Diesel engine.
2. Description of the Related Art
In a conventional exhaust emission control device, as disclosed in Japanese Unexamined Utility Model Publication No. 62-5820, a particulate filter is provided in an exhaust system, and a filter for removing an offensive odor component such as aldehydes from the exhaust gas is provided downstream of the particulate filter. This filter for removing an offensive odor component is constituted by coating an offensive odor absorbing agent such as .pi.-alumina on a cordierite substrate, and carrying a catalyst such as platinum and palladium on an end portion of the substrate downstream of the coated portion. The offensive odor component is absorbed by the absorbing agent at a low temperature, and then is separated from the absorbing agent at a high temperature to be oxidized by the catalyst and discharged to the atmosphere together with an offensive odor component such as unburnt hydrocarbons (HC) discharged from the engine, which HC is also oxidized by the catalyst.
In the conventional exhaust emission control device, since the offensive odor removing filter is manufactured by applying the catalyst on an end portion of the filter, which is constituted coating the absorbing agent on a surface of the cordierite substrate, the manufacturing process is complicated. But, if the absorbing agent and the catalyst are provided on different substrates, another container for housing a catalyst must be provided, and thus the construction is complex. Further, since an air-fuel ratio of the exhaust gas of a Diesel engine is usually lean, the above described exhaust emission control device cannot remove nitrogen oxides (NOx).